Computerized axial tomography ("CAT") or computerized tomography images an axial section of a patient by obtaining a series of different angular projections of the section and reconstructing a two-dimensional image from the series of one-dimensional projections. In contrast to conventional tomography and radiology, x-rays do not pass through the adjacent anatomy, only through the section of interest.
Contemporary scanners are of the third- or fourth-generation variety. The third-generation design is a "rotate-rotate" scanner, in which the tube and detector array are directed opposite each other and are both rotatable movable around the patient. The fourth-generation systems rotate the x-ray tube, but keep the detector array stationary.
With the advent of third and fourth-generation CT scanners, invasive and interventional procedures that are performed under CT guidance are now used extensively. CT-guided needle aspiration biopsies have been highly successful and have alleviated the need for diagnostic surgery in many cases. In addition, CT now guides the percutaneous drainage of abdominal abscesses, reducing the need for repeated surgery. Until recently, however, all of these procedures were guided manually, causing the process to be time consuming and also requiring multiple needle manipulations and repeat scannings to verify needle placement.
Magnetic Resonance Imaging, MRI, is a method of using low energy electromagnetic radiation rather than high energy x-rays to produce diagnostic medical images. By varying magnetic fields and the emission of radio waves, signals can be produced and reconstructed into two or three dimensional images. MRI technology is commonly used to provide information in a format similar to computed axial tomography but with unique flexibility in choosing the reconstruction plane. Equipment used with a magnetic resonance scanner must be nonferromagnetic so as not to interfere with its operation.
There are certain medical conditions, such as some types of metastatic liver cancer, that can be evaluated only with MRI. Furthermore, because of anatomic considerations, different planes than the axial may be needed to direct biopsies. No existing biopsy device meets the three dimensional or nonferromagnetic needs of MRI directed procedures.
CT stereotaxis is a well-established procedure for the head. The bony skull, with its consistent relationship to the brain, allows attachment of a rigid frame. In such devices, reference coordinates from which various entry paths are calculated are taken from the attached frame itself rather than from the patient's skin.
In CT-Guided Stereotaxic Biopsy Of Brain Tumors: New Technology For An Old Problem, H. Black, A. Mechanic and R. Markowitz, 10(4) Am. J. Clin. Oncol. 285 (1987), for example, a metal base ring for fixation to the skull with localizing rings consisting of carbon fiber rods arranged vertically and diagonally is disclosed. The carbon rods of the localization rings appear on the CT scan to enable localization of the lesion. The biopsy probe-carrier is attached to an arc guidance system which is applied to the base ring fixed upon the patient's head. The arc system enables positioning of the probe at any angle in a single plane.
In Preliminary Experience With Brown-Roberts-Wells (BRW) Computerized Tomography Stereotaxic Guidance System, P. Heilbrun, T. S. Roberts, M. L. J. Apuzzo, T. H. Wells, and J. K. Sabshin, 59 J. Neurosurg. 217 (1983), a stereotactic system consisting of a head ring, a localization system, an arc guidance system, a phantom simulator, and a forstan are disclosed for use in stereotaxic guidance on the skull.
U.S. Pat. No. 4,463,758 discloses a stereotactic frame designed for use with a CT scanner. The frame comprises a platform including an area for supporting a patient's head and for maintaining the patient's head in position. The support is provided with pins that may be threadably extended to engage the patient's head. An inverted, substantially U-shaped frame is pivotally mounted on the support. A probe holder is movably mounted on either the leg portion of the U-shaped frame or the base portion of the U-shaped frame.
In U.S. Pat. No. 4,592,352, an apparatus for performing surgical procedures through a patient's skull to a target within the skull by utilizing CT and NMR scanners is disclosed. The apparatus includes a base platform and a pair of vertical support members on opposite sides of the base platform. A head holder is mounted on the base platform to accommodate the patient's head. The head holder includes screws that extend inwardly therefrom for engaging the patient's skull. An arc carrier is pivotally mounted to arc carrier supports and has an arcward segment movably mounted thereon. A probe holder is further selectively mounted on the arc carrier. The apparatus is free of artifact and may be moved to any desired angle. The probe holder on the arc carrier may be rotated to any desired angle so as to reach the target through any point on the skull.
Unlike the skull, the body does not have a consistent relationship of its surface anatomy to the underlying organs. Many of the organs within the thorax and abdominal cavities move with respiration so that changes in the phases of respiration affect the spatial relationship of organs to the superficial soft tissue. Furthermore, there is no structure to which a rigid frame can be attached.
A handheld guidance device for use in conjunction with a CT scanner which allows a user to place a probe within a patient's body at a desired angle is disclosed in U.S. Pat. No. 4,733,661. The guidance device includes a generally planar base including a bubble level to aid in maintaining the base horizontal. A needle support arm is pivotally attached to the base. A cooperating protractor indicates the relative angle of the needle in relation to the base. The accuracy of probe placement obtainable with such a handheld device is severely limited, however.
U.S. Pat. No. 4,583,538 discloses a method and apparatus allowing CT guided biopsies of the body. The method is based upon finding a reference point on the patient's body that exactly correlates to a point on the CT scanner. Locating the reference point is accomplished by means of a localization device placed on the patient's skin. The localization device can be identified in the cross-section of a CT scan. Measurement of the localization device on the CT scanner is then correlated to the device on the patient.
A device which allows angular rotations about the X, Y and Z axes to enable any orientation of the needle direction to be set for penetration is also disclosed. The device has two moving members that provide displacements in the Y-axis direction. X-axis movement is accomplished by an X-travel bar and Z-axis movement is accomplished by a Z-travel bar. Angular rotations about these axis enable any orientation of a needle direction to be set for successful guidance to a target. The multiple axes of such a device maximize torsion within the system, however, thereby severely limiting the accuracy of needle placement. The stability of the system is also decreased because the force applied to the probe is tangential to the support. Stability and reproducibility are especially essential in MRI applications. An additional source of inaccuracy arises in that the interface of the device with the biopsy needle does not allow constant guidance into the target.
In an attempt to address the problem of the change in spatial relationship of internal organs of the body to the superficial soft tissue with change in the phase of respiration, U.S. Pat. No. 4,583,538 discloses a respiratory gating device. The gating device employs a water and tube strain gage that is wrapped around a patient's chest and subsequently connected to a transducer. The transducer gives a digital representation of the patient's phase of respiration. This indirect measurement of respiratory volume introduces significant error, however, which can result in the need for multiple needle insertions to successfully localize a mass lesion. A major source of such error is the vast number of forms and sizes the human chest may take.
Inaccuracy in depth measurement of a biopsy needle as a result of soft tissue compression is another problem experienced with current stereotactic procedures performed on areas of body other than the head. Error from soft tissue compression in combination with the variation in axial position resulting from respiratory variation can result in the need for multiple needle insertions even with CT or MRI guidance using current stereotactic procedures. Multiple needle insertions increase the risk of bleeding and infection as well as the risk of inadvertent puncture of other internal organs and vascular structures. Improper needle localization in the chest, for example, can cause partial or complete collapse of a lung.
Still a further problem in current stereotactic procedures is the difficulty in maintaining the needle and lesion in the same plane of a CT or MRI section. This can result in the over-utilization of time to locate the tip of the biopsy needle to ensure that the biopsy needle has penetrated the lesion, thereby increasing both medical costs and patient anxiety. Additionally, complex approximation of angles within the plane of section result in further over-utilization of time and increase the likelihood of error.
Still a further problem encountered with MRI stereotactic applications is the need to provide greater accuracy and to reduce the scanner time required. In MRI applications, realignment of the needle and confirmation of its position can require impractical periods of time if not done efficiently.
Accordingly, an object of the present invention is to provide a stereotactic biopsy device that eliminates or minimizes the above problems while imparting a greater level of physician confidence in interpreting biopsy results.